Method for recording fingerprints

ABSTRACT

A method of recording fingerprints whereby the finger is coated with a reducing agent, electro-oxidation products are generated on the ridges of the finger and the finger contacted with a recording substrate containing an indicator for the electrooxidation products.

nite States Patent [1 1 Williams et a1.

[73] Assignee: RCA Corporation, New York, N.Y.

[22] Filed: Sept. 21, 1973 [21] Appl. No.: 399,482

[52] 11.8. CI. ll7/0.5, 118/315 [51] Int. Cl A6lb 5/10 [58] Field ofSearch 1l7/0.5; 118/315 [56] References Cited UNITED STATES PATENTS1,170,273 2/1916 Jorgensen 117/0.5

[ Feb. 18, 1975 2,715,571 8/1955 Oden ll7/0.5 3,305,459 2/1967 Smith eta1 204/18 3,549,253 12/1970 Brodie l17/0.5 3,677,786 7/1972 Hollmann eta1. 1l7/0.5

Primary Examiner-Michael Sofocleohs Attorney, Agent, or Firm-Glenn H.Bruestle; Birgit E. Morris [5 7] ABSTRACT A method of recordingfingerprints whereby the finger is coated with a reducing agent,electro-oxidation products are generated on the ridges of the finger andthe finger contacted with a recording substrate containing an indicatorfor the electro-oxidation products.

6 Claims, 2 Drawing Figures 'n Ill (8 6 4* TIMER I r x /7 STAMP PADELECTRODE ELECTRODE SUBSTRATE TIMER SUBSTRATE TIMER ELECTRODE ELECTRODESTAMP PAD 0O 2 HW NL 4 2 O 23 /V mm E D 0 R T... C H m/ 2 70 E D O R T E2H 1 METHOD FOR RECORDING FINGERPRINTS BACKGROUND OF THE INVENTIONFingerprinting has been recognized for several decades as an excellentmeans of identifying one individual from all other individuals. In spiteof many technological advances which have been made in other areas ofidentification, the method of fingerprinting still in most widespreaduse involves a laborious process whereby printers ink or black ink iscoated on an inking slab, the fingers are pressed firmly onto the slabso as to completely coat the fingers with the ink, and then the fingersare pressed firmly onto the substrate upon which the prints are to berecorded. Removal of the ink from the fingers thereafter is a tediousand inconvenient procedure.

One of the characteristics of present day business life is a decreasinguse of cash and an increasing use of substitutes such as checks, creditcards and the like. Unfortunately, this has created an increasedopportunity for forgeries, use of bad checks, fraudulent credit cardpurchases and the like, particularly in view of our highly mobilesociety where local merchants no longer are personally acquainted withtheir customers. Thus the prevention of such crimes is of prime concernto the business community and it would be highly desirable to be able toprovide a method and apparatus for recording fingerprints which isconvenient enough and rapid enough so that a merchant could record thefingerprints of customers making noncash purchases on the spot. Suchrecording would have an inhibiting effect on the would-be criminal, whowould have to leave behind incriminating evidence.

Various methods for recording fingerprints besides the traditional inkmethod have been proposed from time to time, but they have never beenwidely adopted. For example, U.S. Pat. No. 2,299,652 discloses achemical fingerprint recording method whereby the fingers are contactedwith a solution containing a colorless chemical and applied to a paperwhich has been impregnated with an indicator solution. This methodeliminates the use of ink on the fingers but requires special solutionsand a supply of treated paper. This method has the further disadvantagethat the prints are subject to fading and to reversible reactions withcontaminants in the environment.

U.S. Pat. No. 2,736,114 employs a similar method with a paperimpregnated on one surface with an indicator and coated on the othersurface with an adhesive. The adhesive enables the paper having theprint on one side to be affixed to an instrument such as a check ornote. However, the danger of loss or separation of the affixed paperduring handling is apparent.

U.S. Pat. No. 3,408,217 discloses an electrical system for recordingfingerprints whereby a charge is deposited on an insulator in a patterncorresponding to the fingertip ridges by passage of an electric currentthrough the fingers. The prints are then developed using xerographictechniques. However, this method requires bulky equipment which is tooexpensive to be employed by most retain establishments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic arrangement ofan apparatus useful in the present process.

FIG. 2 is a schematic diagram of circuitry which can be employed in theapparatus.

DETAILED DESCRIPTION OF THE INVENTION Although reference is madehereinafter particularly to fingerprints, the method and apparatusherein described is equally applicable to prints of other bodyextremities, such as the foot, palm and the like.

The present method for recording fingerprints comprises the steps of( lcoating the finger with a sensitive reducing agent, (2) passing acurrent through the reducing agent coating so as to generateelectrooxidation products on the surface of the finger and (3)contacting the finger to a recording medium containing an indicator forthe electro-oxidation products. A current can be passed through thereducing agent coating as by pressing the finger to a conductivesubstrate connected to a source of direct current.

A preferred reducing agent-indicator combination which we have found tobe sensitive, reliable and permanent is potassium iodide-starch. Thefinger is first coated by moistening with a solution of potassium iodideor other iodide containing solution. The finger can be immersed in thesolution or, more conveniently, pressed to an absorbent materialsaturated with the solution, such as an ordinary stamp pad.

The coated finger is next pressed to a conductive substrate such as aplate or film connected to a source of direct current. The substrate canbe any conductive surface large enough for the fingers to rest against.Suitable substrates include metal plates having a thin noble metalcoating of gold, silver, platinum or the like, or glass plates having athin, transparent conductive coating of tin oxide or indium oxide. Asecond finger or fingers can be contacted to a second conductivesubstrate to complete the circuit. The finger to be printed is contactedto the positive side of the direct current circuit. The electricalpotential applied to the fingers is on the order of 2030 volts, which issufficient to generate the electro-oxidation products within a shortperiod of time, but insufficient to generate any sensation in the personbeing fingerprinted.

Generation of the current through the finger produces electrochemicaloxidation products on the finger. In the case of potassium iodide, freeiodine is generated according to the equation.

The free electrons pass to the anode.

The finger, now having free iodine on the surface, is then contacted toa recording medium containing an indicator. In the case of iodine,uncoated paper contains sufficient free starch or related compounds toform colored reaction products. Thus when the finger is pressed to anyuntreated, ordinary paper, a dense, high resolution, permanent print ofthe identifying ridges of the finger appears on the paper.

At a potential of about 20-30 volts applied for about 5-10 seconds, acharge of about 0.5 millicoulombs will be delivered, which will in turnproduce a dense, easily readable, permanent fingerprint from theresulting electro-oxidation products. Since the amount ofelectro-oxidation product formed on the finger is directly proportionalto the total charge passed through the finger (current x time), a lowercurrent will require more time to develop sufficient electro-oxidationproducts. If too high a current is employed, of course, it will bedetectable by the person being fingerprinted and may be uncomfortable.The current can be supplied by suitable batteries, or by conversion ofregular electric current in known manner.

The above method is rapid and inexpensive and produces high qualityfingerprints without the need for development and without leaving anycolor or obvious residue on the fingers. Fingerprints can be permanentlyimprinted onto checks, credit card purchase receipts, identificationcards and the like, with minimal inconvenience to the person whose printis taken.

An apparatus useful for carrying out the method described above issimple, compact and inexpensive to make.

FIG. 1 is a schematic arrangement of an apparatus suitable forpracticing the invention. A container for the reducing agent 1, whichcan be a stamp pad, is filled with a aqueous solution of potassiumiodide as the reducing agent. One electrode 2, a tin oxide coated glassplate, is connected to the positive side of a battery 3 by a wire. 4. Asecond electrode 5, also a tin oxide coated glass plate, is connected toa timer switch 6 which in turn is connected to the negative side of thebattery 3 with wires 7 and 8 respectively. The timer 6 turns on uponcompletion of the circuit and allows current to pass through the circuitfor about ten seconds after which it opens the circuit. An audible orvisible signal may then be emitted from the timer 6. A recording element9 can be any uncoated paper substrate, such as a check.

Different persons have differing skin resistance and the same personsskin resistance may vary from time to time, Notwithstanding suchdifferences and variances, it is desirable that approximately 0.5millicoulombs of charge be delivered to the finger to be imprinted so asto develop the desired amount of electrooxidation products thereon.Compensation for such differences and variances may, for example, beaccomplished by providing, in a system having a fixed time period ofcharging, suitable circuitry to automatically provide a predeterminedamount of current flow, i.e., a constant current circuit. Alternatively,compensation may be provided by allowing the current to vary withvarying skin resistance, but automatically providing an adjusted timeperiod of charging in order to obtain the desired total charge.

FIG. 2 is a schematic diagram of suitable constant current circuitry. Asshown in FIG. 2, a first tin oxide coated glass plate 12 is connecteddirectly to the positive electrode of a battery 14. A second tin oxidecoated glass plate 16 is connected to the collector electrode 18 of anNPN transistor 20. The emitter electrode 22 of the transistor isserially connected to the negative electrode of the battery 14 through afirst variable resistor 24 and a timer switch 26. The anode of a Zenerdiode 28 is connected to the juncture between the resistor 24 and thetimer switch 26 and the cathode 5 of the Zener diode 28 is connected tothe base electrode 30 of the transistor. A second variable resistor 32is connected between the tin oxide coated glass plate 12 and thetransistor base electrode 30.

In operation of the circuit of FIG. 2 the variable resistors 24 and 32are adjusted so as to open the circuit when the appropriate amount ofcharge has been delivered.

Although the resistance between the two plates 12 and 16 may vary by afactor of 2-3, the current flowing between the two plates will be onlyslightly affected, thereby providing a predetermined total charge at thefinger in question. Thus, the desired number of molecules of free iodinewill be formed on the finger to be printed in the prescribed time, whichin turn will permit a uniform imprint on the recording mediumindependent of the individual skin resistance.

We claim:

1. A method of recording prints of the body extremities which comprisesa. coating the extremity to be recorded with a reducing agent,

b. passing a current through the reducing agent coating so as togenerate electro-oxidation products on the coated extremity and c.contacting the extremity with a recording medium containing an indicatorfor the electro-oxidation products to fonn a permanent image of saidextremity on said recording medium.

2. A method according to claim 1 wherein the reducing agent is potassiumiodide.

3. A method according to claim 2 wherein the recording medium isuntreated paper.

4. A method of recording fingerprints which comprises a. coating one ormore fingers to be printed with a solution containing potassium iodide,

b. pressing the coated finger or fingers onto a conductive substrateconnected to the positive side of a direct current power source,

c. placing another finger or fingers on a second conductive substrateconnected to the negative side of the power source, thereby generatingfree iodine on the surface of the finger or fingers to be printed, and

d. contacting the finger or fingers to be printed onto astarch-containing recording medium to form a permanent fingerprint onsaid recording medium.

5. A method according to claim 4 wherein the recording medium isuntreated paper.

6. A method according to claim 4 wherein the direct current power sourcedelivers about 0.5 millicoulombs charge to the finger.

1. A METHOD OF RECORDING PRINTS OF THE BODY EXTREMITIES WHICH COMPRISESA. COATING THE EXTREMITY TO BE RECORDED WITH A REDUCING AGENT, B.PASSING A CURRENT THROUGH THE REDUCING AGENT-COATING SO AS TO GENERATEELECTRO-OXIDATION PRODUCTS ON THE COATED EXTERMITY AND C. CONTACTING THEEXTREMITY WITH A RECORDING MEDIUM CONTAINING AN INDICATOR FOR THEELECTRO-OXIDATION PRODUCTS TO FORM A PERMANENT IMAGE OF SAID EXTREMITYON SAID RECORDING MEDIUM.
 2. A method according to claim 1 wherein thereducing agent is potassium iodide.
 3. A method according to claim 2wherein the recording medium is untreated paper.
 4. A METHOD OFRECORDING FINGERPRINTS WHICH COMPRISES A. COATING ONE OR MORE FINGERS TOBE PRINTED WITH A SOLUTION CONTAINING POTASSIUM IODIDE, B. PRESSING THECOATED FINGER OR FINGERS ONTO A CONDUCTIVE SUBSTRATE CONNECTED TO THEPOSITIVE SIDE OF A DIRECT CURRENT POWER SOURCE, C. PLACING ANOTHERFINGER OR FINGERS ON A SECOND CONDUCTIVE SUBSTRATE CONNECTED TO THENEGATIVE SIDE OF THE POWER SOURCE, THEREBY GENERATING FREE IODINE ON THESURFACE OF THE FINGER OR FINGERS TO BE PRINTED, AND D. CONTACTING THEFINGER OR FINGERS TO BE PRINTED ONTO A STARCH-CONTAINING RECORDINGMEDIUM TO FORM A PERMANENT FINGERPRINT ON SAID RECORDING MEDIUM.
 5. Amethod according to claim 4 wherein the recording medium is untreatedpaper.
 6. A method according to claim 4 wherein the direct current powersource delivers about 0.5 millicoulombs charge to the finger.